1. Field of the Invention
The present invention relates to an active balun device, and more particularly, to an active balun device having a sufficient gain and a desired bandwidth in a semiconductor circuit.
2. Discussion of Related Art
Generally, a common source field effect transistor (FET) and a common gate FET are widely used to constitute a wide-band amplifier, characteristics of which are very sensitive to processes and parasitic elements.
In a conventional active balun device, an input signal is provided to sources and gates of common gate and source FETs, and an output signal is derived at drains of the FETs. The signal input to the source is in phase with the output signal at the drain while the signal input to the gate is 180° out of phase with the output signal at the drain. Thus, a phase difference at the two output ports is 180°, realizing active balun. In this case, a change in bias of the transistors connected to the respective inputs and a change in a process leads to a great change in a phase and significantly affects the bandwidth.
Further, such a conventional active balun device has a balun characteristic very sensitive to the bias and sizes of respective devices.
As described above, the conventional active balun device obtains a 180° phase difference using transistors or broadens a bandwidth using an inductor peaking technique in a differential structure, but has a great-sized amplifier due to a change in transistors' performance and the use of the inductor.